This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to Japanese Patent Application No. 2000-197969, filed on Jun. 30, 2000, the entire content of which is incorporated herein by reference.
This invention generally relates to a hydraulic brake apparatus that feeds hydraulic brake pressure to wheel cylinders provided on respective wheels of an automobile. More particularly, the present invention pertains to a vehicle hydraulic brake apparatus provided with a master cylinder section, an auxiliary hydraulic pressure source and a pressure regulating device.
A known hydraulic brake apparatus for an automobile is disclosed in U.S. Pat. No. 5,029,951 (corresponding to a Japanese Patent Application published as Toku-Kai-Hei 2 (1990)-95966). This known hydraulic brake apparatus is provided with a hydraulic pressure booster for assisting activation of the master cylinder in response to the brake pedal depression by using the output hydraulic pressure supplied from a power hydraulic pressure source (the auxiliary pressure source) as an assisting power source. The hydraulic brake apparatus also includes a power piston and the master cylinder possessing diameters that are different from each other, and a closed chamber hydraulically connecting the power piston to the master cylinder. According to the above structure, the brake pedal stroke can be minimized. Further, the master cylinder ran be activated directly by the brake pedal when the hydraulic pressure booster is unable to generate a sufficient assisting pressure force.
The hydraulic pressure booster also includes a one-way valve disposed between the power chamber of the hydraulic pressure booster and the closed chamber. When the hydraulic pressure booster is unable to generate sufficient assisting pressure force, the power piston can be operatively connected to the master piston. A check valve and a cup-like sealing member function as the one-way valve.
Known hydraulic brake apparatus are provided with an assisting apparatus (booster), a reaction force member is provided for attaining a so-called jumping characteristic and a wide range servo ratio. For example, as described in U.S. Pat. No. 4,566,275 (corresponding to a Japanese Patent Application published as Toku-Kai-Sho 58 (1983)-71249), a rubber block is provided with the hydraulic pressure booster as the reaction member. Hydraulic pressure applied to the master cylinder is transmitted to the rubber block as a reaction force via an output member and another element. Accordingly, the rubber block is deformed relative to a thrust portion of the booster.
As described in a Japanese Patent Application published as Toku-Kai-Hei 7 (1995)-108920, a reaction force disc is compressed and deformed under the brake operated condition. The reaction force disc may deform into a clearance defined between a reaction force rod and a guiding hole that slidably receives the reaction force rod. The surface of the reaction force disc may thus be damaged. Therefore, a brake reaction force transmitting apparatus is disclosed for preventing the reaction force disc from entering into the clearance between the reaction rod and the guiding hole and for maintaining a stable reaction force transmitting performance.
More specifically, the brake reaction force transmitting apparatus is provided with the reaction force disc and the reaction force rod. The reaction force disc is formed of an elastic member which is disposed in the hydraulic brake booster and is arranged adjacent to the master cylinder. The reaction force disc urges the master cylinder to be activated in response to the operation of the brake operating member. The reaction force rod is slidably received in the guiding hole defined in the hydraulic brake booster and arranged adjacent to the brake operating member. The reaction force transmitting apparatus serves to transmit the brake reaction force to the brake operating member via the reaction force disc and the reaction force rod. The reaction force transmitting apparatus is provided with a resin member at an end portion of the reaction force rod facing the reaction force disc. Therefore, the resin member is slidably received in the guiding hole as well as the reaction force rod.
In the hydraulic brake apparatus described in the aforementioned U.S. Pat. No. 5,029,951, a large diameter power piston is hydraulically connected to a small diameter master piston via the closed chamber. However, the reaction force member is not disposed between the power piston and the master piston.
In the aforementioned U.S. Pat. No. 4,566,275 and the Japanese Patent Applications published as Toku-Kai-Hei 7 (1995)-108920, the rubber block and the reaction force disc are disclosed as the reaction force member. The front end surface of the rubber block and the reaction force disc is operatively in contact with the rod, wherein a force is always applied to the reaction force member. Therefore, the rubber reaction force members may deteriorate. Particularly when the rubber made reaction force members, including the block and the reaction force disc, are provided for the hydraulic pressure booster, it is preferable that the reaction force member be disposed in a large diameter portion for maintaining durability. In such a situation, the overall hydraulic pressure apparatus must be enlarged.
A hydraulic brake apparatus for a vehicle includes a brake operating member, a reservoir, and a master cylinder for generating brake hydraulic pressure by increasing brake fluid pressure from the reservoir. A master piston is provided in the master cylinder and is movable in response to operation of the brake operating member. A closed chamber is defined by the master piston and a power piston is disposed behind the master piston. A power chamber is defined by the power piston and a rearward portion of the power piston. An auxiliary hydraulic pressure source serves for generating power hydraulic pressure by increasing the brake fluid pressure from the reservoir to a predetermined hydraulic pressure. A pressure regulating device is connected to the auxiliary hydraulic pressure source and to the reservoir, wherein the output power hydraulic pressure from the auxiliary hydraulic pressure source is regulated to a predetermined hydraulic pressure and fed into the power chamber. A reaction force member is disposed in a front end portion of the power piston and is exposed towards the closed chamber. A retaining member is disposed at either the master piston or the power piston, and maintains the reaction force member to be exposed to the closed chamber, wherein the reaction force of the master piston in a rearward direction is transmitted directly to a front end portion of the power piston while bypassing the reaction force member.
The retaining member can be in the form of an intermediate member disposed at the front end portion of the power piston and engageable with the rear end portion of the master piston, with a clearance being defined between the rear end portion of the master piston and the reaction force member when the intermediate member and the rear end portion of the master piston contact one another.
A collar portion can be provided at the rear end portion of the master piston. The collar portion is engageable with the front end portion of the power piston, with a clearance being defined between the rear end portion of the master piston and the reaction force member.
According to another embodiment of the invention, a hydraulic brake apparatus for a vehicle includes a brake operating member, a reservoir containing brake fluid, a master cylinder that generates a brake hydraulic pressure by increasing a pressure of the brake fluid from the reservoir, a master piston provided in the master cylinder and movable in response to operation of the brake operating member, a closed chamber defined at least in part by the master piston, a power piston disposed behind the master piston, a power chamber defined at least in part by the power piston at a rear portion of the power piston, and an auxiliary hydraulic pressure source that generates a power hydraulic pressure by increasing the brake fluid from the reservoir to a predetermined hydraulic pressure. A pressure regulating device is connected to the auxiliary hydraulic pressure source and the reservoir, and regulates the power hydraulic pressure output from the auxiliary hydraulic pressure source to a predetermined hydraulic pressure and feeds the regulated power hydraulic pressure to the power chamber. A reaction disc is disposed at a front end portion of the power piston between the power piston and the master piston, and faces towards the closed chamber. An intermediate member is disposed between the master piston and the power piston to maintain the reaction disc at a position exposed towards the closed chamber. The master piston directly transfers a rearwardly directed reaction force to the front end portion of the power piston while bypassing the reaction force member.